So I've been wanting to up my rat breeding but I have no more rack space so I am looking to build another rack. I plan to build a rack 3-4 tubs wide using the home depot mortar mixing tubs. I have heard people say building multi tub wide with wood isn't the best idea but I plan to use 2x4s upright. I've figured it will take a little less wood to make it as well as take up a little less space. I have seen many multi tub racks using litter pans and my biggest problem right now is what to use as the spacers inbetween the tubs. Each tub's "lip" that would slide on the rails is 1 inch wide. Any suggestions on what to do for the spacers between each tub?